1. Field of the Invention
The present invention relates to a seat suspension device for use in an automotive seat.
2. Description of the Prior Art
In general, jolting or rolling experienced during driving an automobile on a rough road is reduced by use of a seat suspension device which is installed beneath the seat for resiliently bearing the same.
A typical example of conventional seat suspension device of this kind is shown in FIG. 1 of the accompanying drawings, wherein the device as a whole is generally designated by (1), which has a lower frame (2) fixed to the floor (not shown) of an automobile, and an upper frame (3) bearing a seat cushion frame (not shown) to which an automotive seat is mounted.
As shown, a pair of X-shaped links (5)(5') are provided between the lower and upper frames (2)(3) to permit vertical movement of the upper frame (3) relative to the lower one (2). Each of the X-shaped links (5)(5') is composed of two links (6)(7) crossed at a pivot point (8) in a manner rotatable thereabout, such that the first link (6) is at its lower end fixed to a lower fixed spindle (9) rotatably supported on the lower frame (2) and at its upper end connected to an upper movable spindle (10) which is provided with a pair of rollers (10a) for allowing the upper end of the link (6) to move in the longitundinal direction of the lateral bar sections of the upper frame (3), whereas the second link (7) is at its upper end rotatably connected to an upper fixed spindle (11) journalled at the upper frame (3) and at its lower end connected to a lower movable spindle (12) which is also provided with a pair of rollers (12a) for movements of the lower end of the link (7) in a same direction as in the upper end of the first link (6). A torsion bar (13) is arranged centrally of the thus-constructed X-shaped links (5)(5'), passing through the pivot portions (8), with its one terminal portion (13a) being curved and secured at the first link (6) of the X-shaped link (5) in a direction opposite the other terminal portion (13a') which is secured via an adjustment mechanism (15) at the upper part of the second link (7) of the opposed X-shaped link (5).
According to this prior art, when a downward load is applied to the seat suspension device (1), the X-shaped links (5) are lowered, causing both terminal portions (13a)(13a') of the torsion bar (13) to move away from each other, whereby the torsion bar (13) produces an elastic repercussive force via its terminal portions (13a)(13a') against the lowering of the X-shaped links (5) so as to absorb a jolt or vibration of the automobile.
However, such structure of the prior art suspension device is not adaptable for use in a small automobile with limited space and a truck whose floor is generally higher, in that the torsion bar (13) extends transversely and centrally of the suspension device (1), which is a limit against the bottom line of a cushion body laying centrally of the device (1). This means that the bottom line of the cushion body can not be further lowered into the central portion of the suspension device (1), as a result of which the buttocks position of an occupant sitting on the seat is not lowered to a lowest possible level, and therefore it is impossible to design a seat of low seating level that is suitable for use in the small automobile or truck.